3 LATE QUATERNARY POLLEN DIAGRAMS FROM SOUTHERN PATAGONIA AND THEIR PALEOECOLOGICAL IMPLICATIONS

Diagrams of fossil pollen in three deposits postdating glacial recessi on of the last ice age provide an account of late-glacial and Holocene vegetation and palaeoclimate in Southern Patagonia. Sites are mires, located along the Estrecho de Magallanes at Punta Arenas (53 degrees 0 9'S, 70 degrees 57'W) and Puerto del Hambre (53 degrees 36'S, 70 degre es 55'W), and an intermittent lake, some 300 km to the north, at Torre s del Paine (50 degrees 59'S, 72 degrees 40'W). Chronostratigraphy is controlled by 20 radiocarbon dates, the oldest site (Puerto del Hambre ) covering close to 16 000 years. Charcoal from the sites and carbonat e (Torres del Paine), as well as tephra layers and an instance of mari ne incursion (Puerto del Hambre), supply additional data of interpreti ve value. Accompanying the fossil pollen records is a reference survey of modern pollen fallout from 43 surface sample localities. Late-glac ial vegetation during deglaciation consisted mostly of tundra, dominat ed by communities of Empetrum, Acaena, Gunnera, and Tubuliflorae (Comp ositae), under a relatively cold, dry climate. Nothofagus, although pr esent in numbers initially at Puerto del Hambre, did not expand until the close of the late-glacial; at Punta Arenas, expansion of Nothofagu s was episodic, occurring during apparent warmer intervals of the last three millennia of steppe-tundra. Holocene vegetation is depicted at first as a patchwork of Nothofagus woodland and steppe subject to clim ate of relative warmth and limited moisture, except at Torres del Pain e, where moisture levels were apparently higher than at sites to the s outh. Closed Nothofagus forest communities, subsequently, are best dev eloped in the late Holocene under a climate with generally cooler, wet ter parameters. Fire, believed to be caused mostly by Palaeoindians, h as had an important role in shaping vegetation sequences in the Holoce ne. Formidable, however, in the development of vegetation are the lati tudinal displacements/variable intensities of atmospheric conditions c aused by shifting storm tracks of the Southern Westerlies.